The amount of force deliverable at the operative end of a hand tool is often limited by the length of the handle. For example, the amount of torque deliverable by a conventional box wrench is closely related to the length of the handle. Similarly, the compressive force deliverable by the jaws of conventional hand pliers is limited by the length of the handles. To achieve relatively large forces at the operative end of such tools, the handles have to be unacceptably long.
It has long been recognized that significant mechanical advantages can be achieved in tools by the use of fluid mechanics. In pneumatic devices for example, the displacements of the pump can be made much smaller than the displacement of the driving cylinder so that every stroke of the driving pump moves the jaws of a tool only a small increment. In this arrangement, the mechanical advantage achieved is great and large forces can be applied by the operative ends of the tool. It is also well known that due to the substantial noncompressibility of fluids, hydraulic tools can achieve greater operative forces than pneumatic tools. However, whereas pneumatic tools can be easily detached from a compressed air source, hydraulic tools must be continually attached to the hydraulic source to prevent loss of hydraulic fluid and introduction of air into the hydraulic circuit. In large hydraulic tools, these problems can be overcome with the use of valves, plugs, et cetera. In smaller tools, this practice is unacceptably inconvenient and mechanically difficult to execute and therefore requires that hydraulically operated hand tools carry their hydraulic fluid and power source on board. Due to these requirements, hydraulic hand tools are typically bulky, unwieldy and difficult to use.
Representative of such tools is the hydraulically operated hand tool disclosed in U.S. Pat. No. 3,058,214 issued to Mekler. The tool has a pressurized fluid reservoir which supplies a pump with fluid through a series of one-way valves for driving a piston. The driving piston operates a pivoting jaw. The tool hydraulic circuit within the complex and requires integrity of each valve to insure proper operation of the tool. Due to the complexity and consequent cost of the tool, these types of tools have not achieved significant commercial success. Failure of any one of the valves renders the tool inoperable. Furthermore, since the valve seats are typically formed as part of the tool body, the entire tool must be returned for repair of a single valve or other mechanism fails.
Another disadvantage of the hydraulic hand tool described is that the displacement of the pump mechanism is fixed. Therefore, a hydraulic hand tool which has a large mechanical advantage, that is wherein the surface area of the pump piston is relatively small as compared to the surface area of the driving piston, delivers a large amount of force to the jaws of the tool but is very slow to use. In such a tool, each stroke of the pump handle only moves the jaws of the tool a small increment. A large amount of power is delivered to the object in the jaws, but the tool requires a large amount of time to bring the open jaws of the tool onto the object. If the mechanical advantage of the hydraulic system is decreased so that the jaws close more quickly on the object therebetween, the amount of force deliverable by the jaws is correspondingly reduced.
Another disadvantage of the described tools is that each tool must be manufactured with its own individual hydraulic mechanisms since it is an integral part of the tool itself. This increases the cost of manufacture for a variety of tools. Furthermore the valve and pump mechanisms of one tool cannot easily be substituted for a malfunctioning pump or valve of another tool.
Thus, a need exists for a family of hydraulic tools which utilize substantially interchangeable hydraulic mechanisms, which have a large mechanical advantage and which are quick and easy to use.